This invention deals with an improved sharpening device and is defined in the environment of cutting convolutely wound logs of tissue or toweling product, and more particularly, its advantageous use on a log saw according to U.S. Pat. No. 4,041,813. While described in this environment, it will be recognized that the same principle of flexure spring-steel mounting and adjustable pre-set pressure with pneumatic unloading can be applied in numerous devices that require very light pressure engagement of the grinding stones to a blade being sharpened on an intermittent sharpening basis.
Cutting of logs made from tissue and toweling paper webs has been known for many years and proceeded from reciprocating to orbital type log saws as defined, for example, in U.S. Pat. Nos. 3,213,731 and 3,292,470. In these earlier log saws, the grinding stones were mounted on a driven rotating shaft which was moved in an axial direction to force the grinding stone against the blade during a sharpening cycle. Actual movement of the shaft was usually activated by pneumatics. However, the static or "break away" friction was often high enough that once activated, the resultant force of the stone against the blade resulted in heavy grind pressures and premature wear of both the grinding stone and blades. Given the presence of oil spray mist, paper dust, and abrasive stone dust, each of the pneumatic cylinders actuating discrete grinding stones operated differently with the result that unequal pressures could be applied to each side of the blade resulting in unequal taper. Driven grinding stones mounted on pneumatically operated slidable shafts represented the state of the art for many years.
In recent years, and as production output from log winders increased, a newer type of orbiting saw having two blades mounted on a common orbiting arm and as described in U.S. Pat. No. 4,041,813 entered the commercial market. Further, the advent of grinding stones having a thin layer of cubic boron nitride resin bonded to the underlying grinding wheel made it possible to eliminate the driving means because this abrasive facing material was very hard and durable and hence was not prone to spot wear during the first few moments of grind when it is essentially non-rotating--see U.S. Pat No. 4,173,846. Free to rotate, the non-driven grinding wheel soon begins to spin, resulting in wear that is uniformally and evenly distributed over the entire annular surface of the grinding face. On earlier models of log saws according to U.S. Pat. No. 4,041,813, the driving means was eliminated, but the idling shaft and grinding stone were still urged against the blade by pneumatic force, and hence unequal grind pressures on each of the stones and heavier than desired grinding pressures were involved. For initial setup, the grinding face was brought into contact with the blade and then adjusted against the blade until it deflected approximately 0.005". This resulted in a moderately heavy grind pressure at the start and established a very limited range of movement (and pressure). With the heavy pressures, the blade wore away quickly and the 0.005" deflection quickly diminished to the point where a new adjustment and positioning was required. In other words, frequent adjustment of the stone grinding positions was involved. When sawing logs comprising thin cores and soft tissue grades rather infrequent sharpening is required, but on tissue grades that are wound more firmly and/or having thicker cores with clay coatings, etc., the sharpened blades became dull faster and hence, the sharpening cycle time decreased. When originally set up to deflect the blade 0.005", and adjustable stop or "limit of travel" insured that greater deflections and heavier pressures would be avoided. When denser or harder to cut stock was involved, operators frequently adjusted the grinding wheel to deflect the blade greater than 0.005" in order to extend the interval of time between adjustments, and with higher than recommended grinding pressures, scalloping of circular blades became a problem. Scalloping refers to the tendency for the circular blade to have "segmented flats or chords" at the periphery and hence, it is no longer perfectly circular. This effect not only decreased the quality of the cuts, but drastically reduced the life of the cutting blade as well as the abrasive facing on the grinding wheel used to sharpen it.
In essence, the original sharpening device used on saws according to U.S. Pat. No. 4,041,813 was "positioned" as opposed to "pressure regulated" and because of the frequency required for adjustment of the grinding assembly and other limitations, a new grinding means was required.
One of the primary objectives of this invention is to overcome the resultant heavier grind pressures generated by the pneumatic pressure required to overcome static friction. Another important aspect of this invention was to have a substantially frictionless device so that very light grind pressures could be applied equally on each of the grinding stones to maintain the same bevel on each side of the blade. The inventive grinding device overcomes several of the above-mentioned problems by allowing very light grinding pressures without significant blade deflection, provides uniformly light pressure over a much wider range of grinder actuation and adjustment, and hence, requires much less frequency of adjustment and less down time of the log saw and upstream rewinding equipment. Benefically, the lighter pressure results in elimination of scalloping while providing longer blade life, and longer life of the boron nitride facing on the grinding wheels. In addition to these benefits, uniformly high quality cuts are produced. Other objectives will become evident in the detailed description of the invention.